Lightweight concrete, also known as EPScrete (expanded polystyrene concrete), is a material widely used in the building of environmentally "green" homes. The substance is often made using small Styrofoam balls as a lightweight aggregate instead of the crushed stone that is used in regular concrete. While it isn't as strong as stone-based concrete mixes, it has several advantages over the more traditional mix. EPScrete has increased insulation properties, and because it's up to 88 percent lighter than stone-based concrete, it has smaller structural support needs such as foundation sizes and steel reinforcement requirements.
Place 5 gallons of water into the concrete mixer. Add in any additive or colorant you wish to use in the concrete, and mix the add-ins thoroughly with the water.
Add half a 94 lb. bag of Portland cement to the mixer as well as the 5 gallon bucket of sand. Mix thoroughly with the water, creating a mix that's soupy in texture.
Add one of the 5 gallon buckets of Styrofoam beads. Mix for a full minute to allow the beads to absorb the water before adding additional buckets of Styrofoam.
Continue adding the Styrofoam, taking the time to mix in each bucket after the addition to the cement mixture. The Styrofoam will quickly absorb the water in the mix. If the mix becomes too stiff to incorporate the beads, add additional water as needed.
Stop mixing the concrete when all the Styrofoam has been absorbed. The mixture should be of a low-slump variety, pourable but not overly soupy.
Pour the mix into molds or forms and place on a level surface covered with plastic film to begin curing. If using as a slab or wall material, pour directly into place and leave it to cure.
Remove the cement from the mold after 24 hours and allow the EPScrete to complete the curing process. Curing should take a full month, and the stone will need to be kept damp during the process in order to allow full strength bonding to occur.